The art of locks and latches is an old art and a very large number of designs have been developed over the years for the purpose of locking or unlocking a door with respect to a supporting structure. Particularly in the art of applying locks to large doors, such as truck doors and garage doors, the mechanism required often becomes large and hence subject to a substantial amount of friction opposing movement of same. In response to this, it is known to mount resilient biasing means within a lock, tending to urge the locking mechanism in a selected direction, as the opening direction, and sufficient that the manual effort required to effect movement in such direction is at a minimum and may not be required at all.
It is further known in such art to apply resilient biasing means to the mechanism holding the lock mechanism in lock maintaining position. It is desirable, however, that while such force should be sufficient to prevent the lock from becoming loose under normal operating conditions, such as road shock in a truck or from blows applied to a door lock by would-be lock breakers, nevertheless it is still desirable that such holding means be capable of being retracted or rendered inoperative by the application of a relatively small force in the proper manner, such as by an operating lever or by a key.
In prior known locks, these problems have been recognized and dealt with and many prior-known locks have been generally satisfactory for their intended uses. One such lock is represented by Boyles U.S. Pat. No. 3,163,033, assigned to the same assignee as the present invention. While as indicated this lock is generally satisfactory, the spring force which assists the opening movement of the bolt is applied to said bolt through the crank and it is applied to the crank at both an awkward angle and at an adverse lever relationship and hence cannot achieve the most efficient results. Particularly, the angle at which such spring force is applied to the crank is at its most inefficient angle at the point of starting the bolt out of its unlocked position, namely the point at which there is the maximum friction resisting such movement. This results either in considerable manual force being required when the bolt is withdrawn from locked position or, if the spring is strengthened to assist this situation, then the force which must be manually applied to overcome such spring when the lock is returned to locking position is greater than desirable.
Another illustrative patent is Hallgren U.S. Pat. No. 3,306,086 wherein such biasing force is applied by a coil spring arranged around the mounting shaft for the crank. Since the lever arm at which such spring force is applied is even shorter than that in the Boyles patent above mentioned, the same situation as above described in connection with the Boyles patent exists here also.
Therefore, in a continuing effort to improve locks of this nature, the present invention has addressed itself to the points above mentioned as well as to others.
Accordingly, the objects of the invention include:
1. To provide a lock particularly applicable to large doors, such as truck and/or garage doors, wherein a resiliently applied force can be utilized for assisting the moving of a locking bolt from a first, as locked, position to a second, as unlocked, position and wherein such force will be applied to said bolt with such efficiency that it can be of minimum magnitude whereby to require a minimum manually applied force for overcoming same for effecting movement of said bolt in the reverse direction.
2. To provide a lock, as aforesaid, in which the adverse lever relationships previously existing between the means generating such resiliently applied force are eliminated and such force is applied to the bolt in a more efficient manner for the purposes aforesaid.
3. To provide a lock, as aforesaid, in which such resilient force is applied in a lineal direction directly onto said bolt.
4. To provide a lock, as aforesaid, having a latch providing interference with appropriate means on the bolt for holding same against movement out of its locked position in response to said resiliently applied force wherein the surfaces effecting said interference are sufficiently small that, while effective, the latch can be easily moved out of its bolt holding position by a relatively small force applied to the latch.
5. To provide a lock having the advantages aforesaid with a minimum of structural change over locks presently known so as to require a minimum of new tooling and to be capable of easy fabrication for either left hand or right hand assembly and installation.
6. To provide a lock, as aforesaid, which will be of simple construction, sturdy, highly resistant to damage by vibration or blows, and capable of long and reliable use under adverse conditions.
Other objects and purposes of the invention will be apparent to persons acquainted with devices of this general type upon reading the following specification and inspecting the accompanying drawings.